Electronic Energy Loss of Heavy Ions and Its Effects in Ceramics

Energy loss of medium energy heavy ions (i.e. Cl, Br, I, and Au) in thin compound foils containing light elements (i.e. silicon carbide and silicon dioxide) is directly measured using a time-of-flight elastic recoil detection analysis (ToF-ERDA) technique. An improved data analysis procedure is proposed to provide the experimentally determined electronic stopping powers. This analysis procedure requires reliable predictions of nuclear stopping. Thus, the nuclear stopping predicted by the Stopping and Range of Ions in Matter (SRIM) code is validated by measuring the angular distribution of 1 MeV Au ions after penetrating a thin silicon nitride foil, using a secondary ion mass spectrometry (SIMS). In order to validate our derived electronic stopping power values, Rutherford backscattering spectrometry (RBS) and SIMS are utilized as complementary techniques to measure the depth profiles of implanted Au ions in SiC. Moreover, the original version of the SRIM code, TRIM-85, is modified to adopt our derived electronic stopping powers to predict ion distributions. The comparison studies show that the ion distributions predicted based on our derived electronic stopping powers agree well with the experimental results, but exhibit considerable discrepancies with the SRIM predictions.

The large deviation from SRIM predictions is further observed in other materials. The distributions of implanted Au ions with various energies from 1 to 15 MeV are measured in Si and MgO. The electronic stopping powers for Au ions in Si are estimated based on the measured ion profiles. For Au ion irradiation in MgO, significant channeling effects on the ion and damage profiles are observed for the irradiations along both axial and planar channels.

Furthermore, the effect of electronic energy deposition from medium energy heavy ions (i.e. 21 MeV Ni) on the damage evolution in MgO, in which the initial defects are induced using 1 MeV Au, is studied. The evolution in damage level and damage structure under the irradiations is characterized using RBS/ion channeling technique combined with transmission electron microscopy (TEM).